Lysosomal hydrolases of neutrophils have an important role in the defence reaction of organisms against tissue damage caused, for example, by microbes or inflammation.
Elastase and cathepsin G, which are neutral serine proteinases existed locally in azurophil granules play a part in the decomposition of connective tissue.
In particular, elastase degrades elastic connective tissue by cleaving the cross-linking of elastin which directly maintains the elasticity of e.g. lung issue, by cleaving the hydrophobic part of protein [J. Cell. Biol., 40, 366 (1969)] and selectively degrading the cross-linking of collagen as well as elastin [J. Biochem., 84, 559 (1978)]. It also acts on tissue proteins such as proteoglycans [J. Clin. Invest., 57, 615 (1976)]. It will be seen therefore that, elastase plays an important role in the metabolism of connective tissue.
Elastase is inactivated by .alpha..sub.1 -proteinase inhibitor (.alpha..sub.1 -Pl) which is a common inhibitor for serine proteinases in vivo and an imbalance of enzyme and inhibitor causes the destruction of tissue [Schweiz. Med. Wshr., 114, 895 (1984)].
The turnover of elastin in normal tissue is very slow [Endocrinology, 120, 92 (1978)], but pathological acceleration in degradation of elastin is found under various diseased conditions such as pulmonary emphysema [Am. Rev. Respir. Dis., 110, 254 (1974)], atherosclerosis [Lab. Invest., 22, 228 (1970)] and rheumatoid arthritis [in Neutral Proteases of Human Polymorphonuclear Leukocytes, Urban and Schwarzenberg, Baltimore--Munich (1978), page 390], which suggests a relationship between elastase and diseases [Infection Inflammation Immunity, 13, 13 (1983)].